Philip the Handsome and Joanna the Mad of Castile were his parents. His grandparents on his mother's side were Ferdinand II of Aragon and Isabella I of Castile. Their marriage made Spain into one kingdom. His grandparents on his father's side were Emperor Maximilian I and Marie, Duchess of Burgundy.

His Majesty or His Imperial Majesty was first used when he was king. His Empire became large and was known as "in which the sun does not set". He was also known as "The Emperor of Universal Dominion."